1. Field of the Invention
The present invention relates to a railway axle equipped with orientable or pivoted wheels and which is of variable width. The axle comprises two side bars articulated to an axle cross member carrying a vehicle body, so that it is able to pivot directionally and also is able to be inclined in a vertical plane, so as to allow each wheel carried by the side bars to follow the curvatures of the railway track and to negotiate unevennesses in the track.
The invention finds its main application in vehicles running on rails in a local network, especially when the rails include tight bends or curves. The invention makes it possible to lower at least a portion of the floor surface of the body of the vehicle over the entire length of the body.
2. Description of the Prior Art
Various types of articulated railway bogies are known, in which the wheels which are mounted either on an axle body or on articulated side bars that are capable of swinging independently about vertical pivots so as to be oriented either separately and freely, or simultaneously and in a coordinated manner, tangentially to the curvatures of the track.
Document EP-A-0,144,821 discloses a bogie in which axles with orientable wheels are directionally integral with the track, these axles assuming an oblique position with respect to the track without being oriented towards the same instantaneous center of rotation. This assembly tends to increase the clearance between the wheel flanges and the rails and to decrease the clearance between the wheel flanges and the safety rails.
Such bogies can only be used on tracks with a large radius of curvature or on tracks without safety rails, such as the tracks used for railways and underground lines, and, possibly those used for trams running on a separate roadbed.
Also, documents BE-A-8700527 and EP-B-0,348,378 disclose bogies with articulated side bars equipped with a device making the spacing between the wheels and the width of the track a constantly good fit. Each side bar consists of two sections articulated about vertical pivots, each section carrying at least one wheel and being directionally controlled by a system of linkages assembled with ball joints.
On curved track, the sections of each side bar pivot with respect to the cross member and with respect to one another, while the cross member remains perpendicular to the axis of the body of the vehicle, so as to orient each wheel flange tangentially to the portion of curved track or parallel to the portion of straight track on which it bears.
The side bars of the bogie which is described in the first document pivot horizontally about two separate pivots which are fixed with respect to the cross member and the result is that the distances between the planes of the left-hand and right-hand wheels decrease progressively when beginning to run in a straight line in order to reach, in tight curves or bends, values which are incompatible with those of the track.
The bogie of the second document makes it possible to keep the clearances and the tolerances between the wheel flanges and the rails on the one hand and the safety rails on the other hand constant by virtue of a pivot off-centering device. Such a bogie must, however, be somewhat over-engineered in order to provide sufficient transverse stiffness between wheels mounted in a canti-lever manner. This increase its weight and cost.